1. Field of the Invention
This invention relates to an improvement in aqueous stripping compositions particularly useful for stripping paints, varnishes, enamels, photoresists and the like, from various substrates. More particularly, the invention relates to improved aqueous stripping compositions comprising polar solvents and organic or inorganic amines by providing a corrosion inhibitor which is gallic acid or a gallic acid ester. The compositions do not include hydroxylamine.
2. Description of the Prior Art
Stripping compositions used for removing coatings from substrates have for the most part been highly flammable compositions, compositions generally hazardous to both humans and the environment and compositions which are reactive solvent mixtures evidencing an undesirable degree of toxicity. Moreover, these stripping compositions are not only toxic but their disposal is costly since they must be disposed of as a hazardous waste. In addition, these stripping compositions generally have severely limited bath life and, for the most part, are not recyclable or reusable.
Generally, compositions containing chlorinated hydrocarbons and/or phenolic compounds or other highly caustic and corrosive materials have been employed as stripping compositions for stripping paints, varnishes, lacquers, enamels, photoresists, powder coatings and the like, from substrates such as wood, metal or silicon wafers. Hot caustic compositions are generally employed to remove coatings from metals and methylene chloride compositions to remove coatings from wood. In many cases, the components of the stripping compositions are relatively toxic reactive solvent mixtures and thus must be subject to stringent use conditions and require hazardous chemical handling procedures and wearing of safety garments and apparel by users so as to avoid contact with the stripping compositions.
Additionally, because many of the toxic components of such stripping compositions are highly volatile and subject to unduly high evaporation rates, the stripping compositions require special human and environmental safety precautions to be taken during storage and use of said compositions.
In photoresist stripping with the use of hydroxylamine and an amine solvent there is the problem with the substrate of titanium etching and aluminum etching. It is therefore desirable to provide a corrosion inhibitor so that such compositions can be used on a various kinds of photoresists.
U.S. Pat. No. 4,276,186 to Bakos et al discloses a cleaning composition which includes N-methyl-2-pyrrolidone and an alkanolamine. However, in a comparative study, applicant has found that the use of N-methyl-2-pyrrolidone does not provide a broad spectrum of cleaning as is capable with the composition of the invention.
U.S. Pat. No. 4,617,251 to Sizensky discloses a stripping composition which is prepared with a select amine and an organic polar solvent. The composition is formed utilizing from about 2 to about 98% by weight of amine compound and about 98 to about 2% of an organic polar solvent.
U.S. Pat. No. 4,770,713 to Ward discloses a stripping composition comprising an alkylamine and an alkanol amine.
U.S. Pat. No. 5,419,779 to Ward discloses a process for removing an organic coating from a substrate by applying a composition consisting of about 62% by weight of monothanolamine, about 19% by weight hydroxylamine, a corrosion inhibitor which includes gallic acid and gallic acid esters, and water.
U.S. Pat. No. 5,496,491 to Ward, which is incorporated herein by reference, discloses a photoresist stripping composition comprising a basic amine, a polar solvent and an inhibitor which is the reaction product of an alkanolamine and a bicyclic compound. However, gallic acid and gallic acid esters are not disclosed as inhibitors.
U.S. Pat. Nos. 5,334,332 and 5,275,771 to Lee disclose a composition containing hydroxylamine, an alkanolamine and a chelating agent. However, the chelating agent is not gallic acid or its esters.
U.S. Pat. No. 5,597,420 to Ward discloses a stripping composition free of hydroxylamine compounds which consists essentially of monoethanolamine and water together with a corrosion inhibitor. The inhibitor includes gallic acid and its esters.
Recently, OSHA, EPA and other similar federal, state and local governmental regulatory agencies have advocated a shift toward use of more human and environmentally compatible stripping compositions and stripping methods that are not subject to the aforementioned drawbacks and problems.
Moreover, heretofore available photoresist stripping compositions have required unduly long residence times or repeated applications in order to remove certain coatings. In addition, various coatings have resisted removal from certain substrates with these heretofore available stripping compositions. That is, these previously available stripping compositions have not provided adequate or complete removal of certain hard-to-remove coatings from various substrates.
It is, therefore, highly desirable to provide stripping compositions that exhibit substantially no human or environmental toxicity, are water miscible and are biodegradable. It is also desirable to provide stripping compositions that are substantially non-flammable, non-corrosive, evidence relatively little, if any, tendency to evaporate and are generally unreactive and also of little toxicity to humans and are environmentally compatible.
Moreover, it would be desirable to provide photoresist stripping compositions that have a high degree of stripping efficacy and particularly such high degree of stripping at lower temperatures than generally required with prior stripping compositions.
It is also highly desirable that photoresist stripping compositions be provided that exhibit substantially no corrosive effects on the substrate, especially those containing titanium and/or aluminum or silicone.
It is also desirable that effective stripping compositions be provided that are devoid of undesirable chlorinated or phenolic components and which do not require the use of hot caustic components. Highly desirable are stripping compositions and use thereof that are not considered undesirable by regulatory agencies overseeing their production and use.
It is also most advantageous that stripping compositions be provided with the above-identified desirable characteristics which evidence synergistic stripping action in that the mixtures of components provide stripping efficacy and stripping results not always obtainable with the individual components for the removal of sidewall organometallic and metal oxide residues.